WEEK1: DIGESTION AND ABSORPTION OF CARBOHYDRATES AND PROTEINS

Question 1

Describe the overview of digestion of Proteins and Carbohydrates from the mouth to the anus.

Answer 1

1.MOUTH
*Salivary amylase
Carbohydrates to maltose

2.STOMACH
*HCL and Pepsin: Protein to Peptides

3. SMALL INTESTINES

***DUODENUM

1.Pancreatic juice
-Trypsin, Chymotrypsin, Carboxypeptidase

**Protein- peptides

2.Pancreatic amylase

**Starch to maltose

***SMALL INTESTINE BRUSH BORDER

3.AMINOPEPTIDASES: small intestine brush border

*Peptide—-Amino acids

4.DISSACHARIDASES: small intestine brush border
disaccharides—Monosaccharides.

Question 2

State the monosaccharides that forms the following disaccharides.

*Maltose:
*Lactose:
*Sucrose:

Answer 2

*Maltose: glucose and glucose
*Lactose: glucose and galactose
*Sucrose: glucose and fructose

Question 3

State the 3 main monosaccharides absorbed in the body.

Answer 3

*Glucose
*Galactose
*Sucrose

Question 4

How does lactose intolerance comes about?

Answer 4

have deficiency in lactase hence cannot break down the disaccharide lactose.

Question 5

Describe the absorption of monosaccharides

Answer 5

1.FROM THE BRUSH BORDER INTO THE CELL
*Glucose and Galactose transported via SGLT SYMPORTER.
-requires energy
-sodium dependent

*Fructose via GLUT-5
-Passive facilitated diffusion.

2.FROM THE CELL INTO THE INTERSTITIAL FLUID
*Glucose, Galactose and sucrose leave the cell via GLUT-5
-Passive facilitated diffusion.

3.FROM THE INTERSTITIAL FLUID INTO THE BLOOD IN CAPILLARIES
*All move into the capillaries by simple diffusion.

Question 6

Describe the absorption of proteins.

Answer 6

Summary:
* The Na/K-ATPase
pump involved in the
absorption of amino
acids.
* Small peptides use a
H+ dependent
mechanism & a
transporter at the apical
membrane.
* Amino acids use a
Na+/amino acid
transporter.
* Overall transport of
amino acid is Na+ &
energy dependent.

Question 7

Describe the absorption of iron.

Answer 7

Summary:
* Dietary iron exists in
heme (animal-based) and
non-heme (plant-based)
forms.
* Heme contains the Fe2+
* Non-heme iron exists in
ferrous (2+) & ferric (3+)
forms.
* Fe2+ is more soluble at
blood pH. Fe3+ is fairly
insoluble at this pH thus
not available for
absorption.
* Fe3+ must be reduced
(converted) to Fe2+ for
effective absorption.
* Use a ferrireductase,
Dcytb
* Divalent metal transporter
1 (DMT1) effects the
uptake of several ions
including Fe2+

Question 8

Monosaccharides Na+-dependent

Amino acids Na+-dependent

Dipeptides H+-dependent

Monoacylglycerols, monoacylphospholipids,
free fatty acids & cholesterol: Lipid soluble & absorbed across enterocyte membrane from micelles formed with bile salts.

Fat-soluble vitamins as monoacylglycerols and others above!

Water-soluble vitamins Na+-dependent

Nucleosides Na+-dependent

Question 9

Summary:
* Protein digestion
starts in the stomach.
* Most (>50%)
absorption occurs in
the duodenum.
* No proteins excreted
as waste.

Question 10

Summary:
* CHOs digestion starts
in the mouth.
* Most (>70%) CHO
absorption occurs in
the duodenum.
* Less than 10% CHO
not absorbed; thus
excreted as waste.